Back Channel or Covert Channel - Computer Definition

Terms used for a computer system
compromised in such a way that it opens a channel for a cracker. Typical back
channel protocols are X-Windows System
and shells such as telnet.
Because these programs are often part of a target’s computer system, attacks
that cannot otherwise compromise the system can nonetheless trigger a back
connection that allows a remote shell.
From a system security point of view, it is important to note that a back
channel will contact the cracker, who must have a fixed IP Address. It is through this procedure that security
sleuths can determine who the cracker is.

This security sleuth information is known to those in the Computer Underground, so more
sophisticated behavior is needed when introducing anonymizers in the back
channel on previously compromised machines. Anonymizers are contacted by the
back channel; they then forward the communication (maybe with further
directions) to the attacker.